How hard is it to flash the International Space Station? It's actually pretty tough to shine one light so that astronauts can see the signal, but the flashy feat was performed for the first time over the weekend.
NASA astronaut Don Pettit discussed the difficulty last month in a blog posting that focused on space station photography:
"Ironically, when earthlings can see us, we cannot see them. The glare from the full sun effectively turns our windows into mirrors that return our own ghostly reflection. This often plays out when friends want to flash space station from the ground as it travels overhead. They shine green lasers, xenon strobes, and halogen spotlights at us as we sprint across the sky. These well-wishers don’t know that we cannot see a thing during this time. The best time to try this is during a dark pass when orbital calculations show that we are passing overhead. This becomes complicated when highly collimated light from lasers are used, since the beam diameter at our orbital distance is about one kilometer, and this spot has to be tracking us while in the dark. And of course we have to be looking. As often happens, technical details complicate what seems like a simple observation. So far, all attempts at flashing the space station have failed."
In today's follow-up post, Pettit reported that the San Antonio Astronomical Association successfully pointed a one-watt blue laser and a white spotlight at the space station early Sunday morning. Pettit had to work out the complicated arrangements for beam diameter, intensity and tracking with the amateur group's members. "Considering that it takes a day, maybe more, for a simple exchange of messages (on space station we receive email drops two to three times a day), the whole event took weeks to plan," he wrote.
Fortunately, it's easier to see the space station than for the space station to see us. When the sun catches the solar arrays just right, the glint can make the orbiting outpost look like a star as bright as the planet Venus, moving from west to east. To find out when and where to look, check out NASA's guide to sighting opportunities.
More views from the space station:
- Aurora extravaganza glows in space
- 'Amazing' view of comet from space
- Cosmic Log archive of space station views
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.